Inferior Rectal Nerve
Inferior Rectal nerve, a branch of the pudendal
nerve, is sensory to the anal canal and surrounding skin. It innervates the sphincter
ani externus muscle.
External hemorrhoids are masses
of dilated tortuous veins that occur below the pectinate line. They are painful
due to the somatic sensory distribution of the inferior rectal nerve. The visceral
sensory distribution above the pectinate line lacks pain fibers; therefore, internal
hemorrhoids are devoid of pain.